Packs of this nature are described in WO 92/20775. The pack contains a prescribed amount of strongly alkaline and hence aggressive cleaning agent, which is apportioned in the dosing unit of washing or rinsing machines, in particular professional machines of this kind. The film surrounding the alkaline solid should protect against contact with the alkaline solid during handling. On the other hand, the film should dissolve or disintegrate in an aqueous alkaline medium by itself, so that separate evacuation and hence handling of such film when or after releasing the solids is not required anymore.
The way of using so-called wash blocks is described in EP-652,724 B1, the contents of which are referred to here.
The general application of packs containing water soluble cleaning agent is affected by problems of physical and chemical compatibility of the films with water and cleaning systems. Many films, for instance those made of polyvinyl pyrrolidine, polyethyl-oxazoline and polyvinyl-alcohol are able to react with active components of a cleaning system. Such films are moisture sensitive and may soften and loose their strength under the effect of the moisture. More important, however, is the fact that many chemicals used in cleaning compounds attack the films and may cause defects in the sealing and/or the water solubility of the pack, particularly if the pack is stored under moist conditions.
In the above mentioned WO 92/20775, several types of films are described. As a rule, multilayer composite films are provided, in which the various layers have a different composition. One of these layers may consist of a copolymer, or a terpolymer of an .alpha.-.beta. unsaturated monocarboxylic acid, possessing a COOH group.
Plastics possessing a COOH-group, which are soluble in aqueous alkaline solution and which are stable in aqueous acid media and generally also in neutral aqueous media, are known in the art. In this context, we refer to the following European disclosures: EP-A-143,935 and EP-A-032,244. From EP-A-314,156, plastics that can disintegrate in neutral aqueous media are also known.